As is known, the development of plants takes place in different stages which are clearly distinct. Examples of such stages are the germination of seeds, the sprouting of perennial plants, the formation of leaves and blossoms and the formation of fruits and seeds. This course of development is genetically determined and is thus influenced by internal, so-called endogenic growth factors.
These endogenic growth factors, however, are in reciprocal relationship to external, i.e. exogenic, growth factors. Examples of these are light, temperature, air, water and nutrients.
Actively growing plants are not very resistant to unfavorable external growth factors such as frost, heat or insufficient water. For the preservation of the species, the plants protect themselves against such fatal external conditions in that the plant parts necessary for the survival of the plants, for example seeds, root stocks, rhizomes, bulbs or buds, pass over into a quiescent stage, the so-called dormancy period. In this state of dormancy, the plants show no externally visible growth, i.e., no sensitive plant parts are formed which could be damaged by unfavorable external conditions.
The beginning and end and thus the period of the dormancy are essentially controlled by environmental factors, such as those set forth supra.
A prolongation of the dormancy offers decisive advantages for the practical cultivation of plants, especially in fruit and grape growing. These advantages are of importance especially under those climatic conditions in which there is still a danger of frost after the commencement of active growth. Such late frosts, which do not occur regularly or with equal severity every year, cause damage to fruit trees and grape vines which have already sprouted and this always involves considerable crop losses.
Attempts have been made to prevent such late frost damage (cf. in this regard, R. I. Weaver, "Grape Growing", pp. 47-55, pub. John Wiley & Sons, N.Y., 1976). Such methods include so-called "frost sprinkling", i.e., the influence of layers of cold air circulated by wind blowers, or the direct heating of orchards. All these methods, which are directed towards the protection of buds and leaves which have already sprouted, are either of only limited effectiveness or are uneconomical because of high energy costs.
Attempts have also been made to prevent late frost damage by prolongation of the dormancy phase with the help of plant hormones (cf. R. I. Weaver, "Plant Growth Substances in Agriculture", pp. 166-167, pub. W. H. Freeman & Co., 1972). Thus, for example, experiments have been carried out with natural plant hormones, such as gibberellin or abscisin, and with synthetic growth inhibitors, such as chlorocholine chloride. These have not given the desired results.
It is, therefore, an object of the present invention to provide a process for prolonging the dormancy of plants or plant parts.
According to the present invention, there is provided a process for prolonging the dormancy of plants or plant parts, wherein the plants or plant parts are treated with an aqueous cyanamide solution before the anticipated sprouting of the plant or plant part.
We have, surprisingly, ascertained that by means of the process according to the present invention, it is possible to achieve considerable prolongation of the dormancy phase. This was surprising because, according to the prior art (see Federal Republic of German Patent Specification No. 31 50 404), a cyanamide solution had precisely the opposite effect, namely, the termination of bud dormancy.
In the case of the process according to the present invention, the cyanamide solution is applied before the anticipated sprouting to plants or plant parts to be treated. Examples of plant parts which can be so treated are buds, rhizomes, corms, bulbs or root stock. The optimum time of treatment is from about 4 weeks to immediately, i.e., about 1 day, before the anticipated sprouting, the time of treatment having a decisive influence on the prolongation of the dormancy. The later the treatment takes place, i.e., the shorter the period of time between treatment and anticipated sprouting, the longer is the delay of the sprouting. In the most favorable case, the prolongation of the dormancy can be up to 14 days. Thus, with the help of the process according to the present invention, it is possible not only to prolong the dormancy in general but also positively to control the period of prolongation by means of the point of time at which the treatment is carried out.
The aqueous cyanamide solution used preferably has a concentration of about 0.05 to about 10% by weight and more preferably of about 1 to about 3% by weight. The cyanamide solution can be applied by means of conventional spraying apparatus and thus has the advantage of a problem-free and readily measurable application.
The amount of cyanamide solution used is preferably such that a complete wetting of the plants or plant parts to be treated takes place. Wetting agents, especially alkylaryl polyglycol ethers, for example "Citowett", may be added to the cyanamide solution, preferably in an amount of from about 0.1 to about 1% by weight, referred to the cyanamide solution.
The process according to the present invention is suitable for the treatment of all plants and especially of fruit trees and grape vines.
The important advantages of the process according to the present invention are the objective control of the prolongation of the dormant phase, simple handling and great economy since cyanamide is an inexpensive chemical. These advantages are the important prerequisites for a safe and economic method for preventing or substantially avoiding crop losses due to late frosts.